1. Field of the Invention
The present invention relates to a method for corrosion prevention and re-etching prevention after an etching process, and more specifically to a method for replacing chlorine atoms on a film layer.
2. Description of the Prior Art
Etching processes can be classified into two types, a wet etching process and a dry etching process. In the wet etching process, a chemical solution is used and an objective of etching is achieved via a chemical reaction. The dry etching process is generally a plasma etching. The plasma etching has an etching mechanism which is basically through a physical interaction, and the most advantageous of the plasma etching is an anisotropic etching. The anisotropic etching can have an etching direction of an etching reaction which is perpendicular to an acting surface, and therefore can avoid an undercut occurrence, so this is more suitable for etching requirements of high aspect ratio and assemblies of a cavity width smaller than 2-3 μm (micrometers).
A chloride gas (e.g., chlorine) is utilized as an etching media in the plasma etching process, and the plasma energy is used to drive a reaction. In other words, the chloride gas is dissociated by the plasma process to form chloride ions, and the chloride ions are bombarded on a carrier's surface to achieve an etching process. However, there are chlorine residuals remaining on the carrier's surface after the etching process, and when the carrier is exposed to atmospheric humidity, the chlorine residuals on the carrier's surface may react with absorbed water to form hydrogen chloride, which has corrosive character, thereby corroding the carrier's surface.
Therefore, a process is proposed where the plasma process is combined with an oxygen gas and a fluorine-bearing gas to replace the chloride ions. That is, the oxygen gas and the fluorine-bearing gas (e.g., sulfur hexafluoride) are passed after the plasma etching, as well as ionize the oxygen gas and the fluorine-bearing gas through the plasma process to replace chlorine atoms on the carrier's surface, thereby preventing corrosion on the carrier's surface. There are two possible ways to replace the above-mentioned chlorine atoms, a first replacement is achieved by two elements having high affinity, for example, when a carrier is an aluminum substrate, the chlorine atoms on a surface of the aluminum substrate tend to be replaced by oxygen ions; a second replacement is achieved by replacing a low electronegativity element with a high electronegativity element, for example, when a carrier is a copper substrate, the chlorine atoms on a surface of the copper substrate tend to be replaced by fluorine ions. These replacement phenomena are selectively chosen depending on relationships between various types of elements in a reactive environment. In the process of replacing the chlorine atoms through the plasma process, the above-mentioned fluorine-bearing gas, such as the sulfur hexafluoride, has a volume ratio which is generally one-tenth to one-sixth of the oxygen gas. However, the fluorine ions of the sulfur hexafluoride having the above volume ratio will result in an etching reaction again to occur on the carrier's surface after dissociation, thereby affecting an electric property of a thin film transistor. Therefore, the conventional process where a plasma process is combined with pure oxygen to replace chloride ions is still widely used in prior art (i.e., a time period for a replacement reaction is generally 30 sec to 45 sec).
Therefore, there is a need to provide a method for improving the prior art, so as to prevent a re-etching occurrence in a plasma process.